Currently used friction reducing systems utilize a process of injecting a high molecular weight friction reducing polymer solution into conduits containing flowing hydrocarbon. The material to be injected is normally extremely viscous and difficult to handle, particularly at low temperatures. Depending upon the temperature of the flowing hydrocarbon and the concentration at which the friction reducing polymer solution is injected, significant time elapses before dissociation and resulting friction reduction occurs. In addition, complex equipment for storage, dissolving, pumping and injecting metered quantities of friction reducing material into flowing hydrocarbon is necessary.
Highly effective friction reducing polymers are described in the art. Representative samples of such art are U.S. Pat. No. 3,692,676 which teaches a method for reducing friction loss for pumpable fluids through pipelines by adding a minor amount of a high molecular weight noncrystalline polymer. U.S. Pat. No. 3,884,252 teaches the use of polymer crumb as a friction reducing material.
The use of high molecular weight polymers as friction reducers for pipelines carrying fluids under turbulent flow conditions is increasing as energy demands increase and power costs increase. Friction reduction is a phenomenon known to depend upon the high molecular weight of the polymer additive and its ability to dissolve in the hydrocarbon under turbulent flow conditions.
One drawback to the use of high molecular weight polymers for friction reduction is their very slow dissolution rate. Solid polymers of these types can take days to dissolve in some cases even though friction reduction is greatly enhanced once dissolution has occurred. This problem can be overcome to a great extent by using solutions of predissolved polymer. However, such high molecular weight polymer solutions become very viscous as the polymer content increases, thus limiting the practical application of these solutions to those containing no more than about 15 weight percent polymer. Additionally, even in this predissolved state, complete polymer dissociation in the flowing hydrocarbon can be slow. The equipment used for injection of the polymer solution can become very complicated and expensive.
Friction reducing polymers, being of high molecular weight, are solids at normal temperatures. Such polymers can be finely subdivided by grinding at very low (cryogenic) temperatures. However, the polymer solids tend to agglomerate as the polymer warms to ambient temperatures. U.S. Pat. No. 4,584,244 discloses that such agglomeration can be prevented by adding inert solids to the friction reducing polymer during the cryogenic grinding process. This patent discloses that the addition of such inert solids e.g. alumina to the grinding process provides a finely divided free flowing polymer slurry which is easily handled and provides rapid dissolution in flowing hydrocarbon oils and subsequent friction reduction.
It would be of great benefit to provide an improved method for placing free-flowing coated particles of friction reducing polymers in flowing hydrocarbon liquids and thereby reducing the friction loss of such liquids.